Brewster's angle

Advanced

Reflected light is fully polarised at this angle.

Key relationtanθ_B = n

At the incidence angle with tanθ_B = n₂/n₁ the reflected light is completely polarised (parallel to the surface). For glass n = 1.5 it is 56.3°.

Worked example

Reflected and refracted rays are perpendicular.

Common mistake

Used in lasers and glare filters.

In more detail

At Brewster's angle, light reflected from a surface is completely polarised parallel to the surface. The angle satisfies tan θB = n2/n1.

Photographers use polarised reflections to reduce glare.
Brewster angle is used in lasers with windows to minimise losses.
Light reflected at Brewster's angle from a glass or water surface is polarised, which is why it is cut by polarising glasses.

What is the Brewster angle for glass?

About 56 degrees from the normal for air to glass.

Why are reflections polarised?

At this angle, the component of light parallel to the surface is not reflected.

How is Brewster's angle found?

Its tangent equals the refractive index of the second medium over the first.